Enhanced Electrocatalytic Activity of Mo-Doped NiFe Layered Double Hydroxide Nanosheet Arrays for the Hydrogen Evolution Reaction

Abstract

NiFeMo layered double hydroxide (NiFeMo-LDH) nanosheet array structures in situ grown on Ni foam were rationally designed and fabricated by a convenient and green hydrothermal strategy. The systematic characterization proved that NixFe1Mo1-LDH/NF (x = 4, 6, 8, 10) composites grew on the surface of Ni foam as vertically interlaced LDH nanosheets. The electrochemical results showed that all composites possessed high electrocatalytic activity, and Ni6Fe1Mo1-LDH/NF exhibited the best hydrogen evolution reaction (HER) performance. Furthermore, the nanosheet array structure with the best active metal molar ratio was in situ grown on reduced graphene oxide (rGO) uniformly modified Ni foam (∼210 nm × 20 nm) with an overpotential of 90 mV at 10 cm–2 in an alkaline solution, which was superior to most non-noble metal-based catalysts. Experimental results and density functional theory with the Hubbard U (DFT + U) calculations confirmed that the active site for H adsorption changed from the Fe site to the Mo site after Mo doping in NiFe-LDH, which reduced the water dissociation energy barrier and the subsequent proton adsorption energy barrier and adjusted the electronic structure of Fe and Ni sites, thereby greatly promoting the whole Volmer–Heyrovsky process under alkaline conditions and improving the HER performance. The synergistic coupling of NiFeMo-LDH nanosheets with rGO enhanced conductivity and electrochemical performance. The growth of NiFeMo-LDH on rGO/NF facilitated the formation of bubbles and significantly improved electrochemical stability. The present electronic regulation strategies using metal doping can be extended to synthesize other types of transition metal composite catalysts and used for the development of renewable and friendly energy devices.